One main problem with static AC-to-DC converters, such as can be used for AC or DC motors, is the generation of harmonics on the AC lines, which are caused by the rectification process. Another problem is cost. The use of transformers and filtering inductances, the rating involved, all require a minimization of components, windings and rectifying devices without losing the benefits of the overall system.
It has been shown in U.S. Pat. No. 4,876,634 of Derek A. Paice how a multiphase AC/DC converter can be designed with a single transformer having successive tappings drawn from a polygonal succession of long and short windings, the difference between outputted currents being derived from the tappings. For the purpose of describing the closest art, the U.S. Pat. No. 4,876,634 is hereby incorporated by reference.